Trump’s support has doubled in the poll since mid-July, when he had at 13 percent support and trailing Bush, who was in the lead at 15 percent.

It’s the latest survey to show the businessman and reality TV star pulling away from the pack of Republican presidential candidates nationally.

Trump now holds a 7.5-percentage-point lead over his next closest competitor in the field, according to the RealClearPolitics average of polls. That lead will increase once the Monmouth survey is factored in.

The Monmouth poll found Trump pulling support from all factions of the party.

Trump has a 20-point lead over Wisconsin Gov. Scott Walker among Tea Party supporters, and leads him by 11 points among those who identify as “very conservative.” Trump has an 8-point lead over Bush, a former Florida governor, among those who identify as “somewhat conservative,” and also leads Bush by 8 points among those who describe themselves as moderates.

Trump leads in every age category, and is the top choice of men and women in the survey.

His favorability rating has improved dramatically with 52 percent saying they have a positive view of Trump, against 35 percent who view him negatively. Before Trump launched his presidential bid in June, only 20 percent had a positive view of him, compared to 55 percent who viewed him negatively.

“Republican support for Donald Trump just continues to grow with no clear sense of who his constituency really is,” said Patrick Murray, the director of the Monmouth University Polling Institute. “This makes it very difficult for his opponents to figure out how to take him on in the upcoming debate.”

Walker is in third place in the poll at 11 percent support, followed by Sen. Ted Cruz (R-Texas) and former Arkansas Gov. Mike Huckabee at 6 percent each. Rounding out the top 10 are Ben Carson at 5 percent, New Jersey Gov. Chris Christie and Sens. Rand Paul (Ky.) and Marco Rubio (Fla.) at 4 percent a piece, and Ohio Gov. John Kasich at 3 percent.

Fox News is capping Thursday’s first presidential debate at 10 based on national polling numbers, and it appears increasingly likely that Christie and Kasich will nab the final two spots on the debate stage.

If that happens, former Texas Gov. Rick Perry is likely to be unlucky number 11. He is tied for 11th place in the Monmouth poll with Carly Fiorina at 2 percent support.

Louisiana Gov. Bobby Jindal, former Sen. Rick Santorum (R-Pa.), Sen. Lindsey Graham (R-S.C.), former New York Gov. George Pataki and former Virginia Gov. Jim Gilmore all took 1 percent support or less in the poll, and will likely be left off the primetime debate stage as well.

Fox News is holding a forum earlier on Thursday for those who don’t make the cut for the main event.

The survey found a plurality of Republican voters aren’t happy with the first debate format.

Forty-five percent said there should be back-to-back debates with the field split randomly between the two, while 29 percent said all of the candidates should be on stage at the same time. Only 23 percent said the debate should be limited to a top 10 based on national polling numbers.

According to the Monmouth analysis, only Trump, Bush, Walker, Cruz and Huckabee are in a defined top tier of candidates, while the candidates in sixth place to 15th place are within the margin of error of the top 10.

“I suppose Fox hoped that a top tier would emerge by the time the first debate rolled around,” said Murray. “But based on current polling, there’s no good rationale for arbitrarily selecting a top 10.”

The Monmouth University poll of 423 registered Republican voters was conducted between July 30 and Aug. 2 and has a 4.8-percentage-point margin of error.